The present invention relates systems and methods for self-calibrating semiconductor devices.
Today's modern electronic products such as computers and high definition televisions rely on advanced integrated circuits (ICs) that operate at high speed. These products in turn rely on a clock source and clock signal that act as a master timing element for control of hardware.
Traditionally, a master clock source is generated off-chip and provided as an input to the ICs. One method for generating the clock signal uses crystals. While this method is well known and is reliable, off-chip generators take valuable circuit board space and have minimum height restrictions. A crystal-based system also requires extra pins for connecting the crystal to an integrated circuit requiring the clock signal. The crystal generator also requires external resistors and capacitors, adding cost, but more importantly takes more board space. Other disadvantages include an inability to operate over extended voltage ranges; long start times when power to the system is turned on; and high power consumption, making the systems less attractive in battery-powered applications.
On-chip oscillators have been designed for applications that demand low cost and low power consumption and applications that can't afford the space or pin requirement that crystal oscillators demand. For instance, ring oscillators have been used in IC designs where an exact clock signal is not required. Large performance variations, however, may be seen by the system as the ring oscillator frequency can vary over process differences, voltage variations and temperature excursions.
Yet another solution that designers have devised is to use of resistor-capacitor (RC) oscillator designs. RC oscillators lack the frequency accuracy of crystal oscillators, but are advantageous in that they can allow instant start-up of the clock signal from a stopped state. They also have low power consumption. However, when using analog electronic components such as those in the RC oscillator, it may be difficult to obtain precise voltages or measurements because analog components have many parameters that vary with process, temperature or power supply. For example, one or more reference voltages for an integrated circuit may be generated from a bandgap reference voltage circuit. If, however, the bandgap reference voltage is not accurate due to variations in power supply or temperature, then all reference voltages derived therefrom will also be inaccurate. This could induce substantial errors in the operation of the integrated circuit.